This application claims benefit of Japanese Application No. Hei 11-201350 filed in Japan on Jul. 15, 1999, the contents of which are incorporated by this reference.
The present invention relates to image pickup apparatus, and more particularly relates to an image pickup apparatus having a static image taking function capable of effectively suppressing blur in the image for example due to camera shake.
It is known in taking a static image with an image pickup apparatus that camera shake or motion of an object causes a blur in the image if the shooting takes a relative long time period. Such xe2x80x9cblurxe2x80x9d in image is also referred to sometimes as xe2x80x9cout of focusxe2x80x9d, since the image is one-dimensionally (including curves) out of focus. In the present specification, however, it will be described as xe2x80x9cblurxe2x80x9d. Although an image blur at times is actively applied in such photographing techniques as panning, it is usually regarded as a degradation of image quality and prevention of this is a must. A typical method for such prevention is to stabilize the camera for example by using a tripod. In another method, a short-time exposure (high-speed shutter) is used. Both, however, are conditionally used and impossible to be applied when the image is to be taken by a hand-held camera in a poorly lighted condition.
A technique as that applicable even to such case has been disclosed in Japanese patent application laid open No. 10-336510. In particular, a motion in object images relative to the imaging surface is previously detected and, on the basis of such information, an optical system (or an imaging block if considered as consisting of an xe2x80x9coptical system+image pickup devicexe2x80x9d) for shifting a formed image is driven when taking images so as to stop object images relative to the imaging surface. Also disclosed in the same laid-open application as known prior art are xe2x80x9ccamera shake correction control meansxe2x80x9d especially for dynamic images. Those mentioned as the correction means include an optical type (using an optical system for shifting a formed image in the above described manner) and an electronic type (shifting an image frame to be extracted from the total imageable area by means of memory and driving of image pickup device). Further those mentioned as xe2x80x9cmethod of detecting camera shakexe2x80x9d include: motion vector detection for detecting the amount and direction of shift of objects by means of image processing; and angular velocity detection for directly detecting the swing of the camera body by an angular velocity sensor.
As pointed out in the same laid-open application, however, the conventional camera shake correction technique for dynamic images is incapable of eliminating image blur in one frame of image when it takes a relatively long time period in taking a static image. In respect of the technique as disclosed in the same laid-open application, it has the following two problems:
(i) Since a special optical system (imaging block) is necessary to shift a formed image, the size/dissipation-power/cost of the apparatus is increased and its image forming performance is degraded due to the use of the special optical system.
(ii) Since correction is performed on the basis of information obtained before the taking of image, the correction becomes erroneous and the image quality gets all the worse if the motion of image has been changed.
To solve the above described two problems in the prior art, it is an object of the present invention to provide an image pickup apparatus having a static image taking function capable of an effective blur correction applicable even to a long-time image taking, without requiring a special imaging block for shifting a formed image in correcting blur, without causing an increase in size/dissipation-power/cost/etc., and deterioration in image forming performance of the apparatus, and furthermore with a capability without requiring a separate sensor of accurate blur correction free from a possibility of erroneous correction even when the motion of image has been changed.
In accordance with a first aspect of the invention, there is provided an image pickup apparatus including: an image pickup device; image signal generation means for generating image signals based on output of the image pickup device; accumulation time control means for controlling charge accumulation time at the image pickup device; pickup image generation means for generating one pickup image signal by adding together a plurality of image signals obtained by rendering a plurality of consecutive exposures by controlling the accumulation time control means; motion information detection means for detecting relative motion information among the plurality of image signals based on the plurality of image signals; and motion compensation means for compensating relative motion among the plurality of image signals based on the detection result at the motion information detection means. The pickup image generation means adds together the plurality of image signals subjected to motion compensation processing at the motion compensation means.
In thus constructed image pickup apparatus, since, in generating a pickup image signal, the plurality of image signals are added together after compensated for relative motion among the plurality of image signals, a special imaging block for shifting a formed image is not required in correcting blur, and an increase in size/dissipation-power/cost/etc., and deterioration in the image forming performance of the apparatus are not caused. Further, since motion information for use in motion compensation is detected on the basis of the plurality of image signals themselves to be added together, a separate sensor is not required and an accurate blur correction is possible free from a possibility of erroneous correction even when the motion of image has been changed. Furthermore, a high-quality, long-time exposure image taking becomes possible with reducing fixed pattern noise. The above object is thereby accomplished.
In accordance with a second aspect of the invention, there is provided an image pickup apparatus capable of obtaining image signals of a plurality of consecutive frames with respect to one image object, including: setting means for setting charge accumulation time per one frame by dividing a set exposure time into a plurality of portions; motion information detection means for detecting relative motion information among the image signals each obtained in the charge accumulation time per one frame; operation means for operating the respective image signals so as to achieve an agreement in object images of the plurality of frames on the basis of output from the motion information detection means; and image generation means for generating one pickup image signal by adding together the plurality of image signals based on the result of the operation.
In accordance with a third aspect of the invention, there is provided an image pickup apparatus capable of obtaining image signals of a plurality of consecutive frames with respect to one image object, including: determination means for determining whether or not a set exposure time is longer than a camera shake limit exposure time; setting means for, if determined as longer than the camera shake limit exposure time, setting the exposure time to a charge accumulation time by which image signals of a plurality of consecutive frames can be obtained; blur detection means for detecting relative amount of blur among image signals respectively for the plurality of consecutive frames obtained with respect to one image object; operation means for mathematically operating vectors concerning the object image between the respective image signals among the plurality of consecutive frames on the basis of the detected blur amount and for mathematically operating amount of shift and direction thereof of the respective image signals so as to achieve an agreement of the vectors; and image generation means for generating one pickup image signal by adding together the plurality of image signals based on the operation result.
In the second or third aspect of the invention constructed as the above, too, a special imaging block for shifting a formed image is not required in correcting blur, and an increase in size/dissipation-power/cost/etc., and deterioration in image forming performance of the apparatus are not caused. Further, a separate sensor is not required and an accurate blur correction is possible free from erroneous correction even when the motion of image has been changed. The above object is likewise accomplished.
The image pickup apparatus according to the first aspect preferably includes blur corrected static image taking control means for, if an exposure time longer than a predetermined value is set, dividing the exposure time into a plurality of exposure periods each shorter than the predetermined value and for setting each of the divided exposure periods respectively as the exposure time of each of the plurality of consecutive exposures. By providing thus constructed blur corrected static image taking control means, the blur correcting function in the image pickup apparatus according to the first aspect can be applied very simply and automatically.
Further, in the image pickup apparatus according to the first aspect, the plurality of consecutive exposures by the blur corrected static image taking control means are preferably performed as equally divided into the least times of exposure on condition that the exposure period of each exposure satisfies the limiting conditions as described above. A higher image taking S/N ratio is thereby achieved at each time and processing concerning detection of motion information becomes simpler and securer.
Furthermore, in the image pickup apparatus according to the first aspect, the predetermined value of exposure time at the blur corrected static image taking control means is preferably set to a camera shake limit exposure time which is determined by the focal length of taking lens and the size of imaging frame. It is thereby possible to apply blur correction under secure conditions backed by the long-standing empirical laws. It is hence always possible even with a zoom camera, etc., to obtain an image without blur under optimum conditions.
Moreover, the image pickup apparatus according to the first aspect preferably includes mode setting means for selectively setting to a first image taking mode where the motion compensation means is caused to function or to a second image taking mode where the same is not allowed to function. By providing such mode setting means, it is easy for the photographer to selectively set a photographing function in accordance with conditions and/or purpose.
It is another object of the invention to provide an image pickup apparatus in which a high-quality, long-time exposure image taking is possible without causing an increase in size/dissipation-power/cost/etc., and deterioration in image forming performance and at the same time with reducing fixed pattern noise.
In accordance with a fourth aspect of the invention, there is provided an image pickup apparatus including: a taking optical system and an image pickup device fixed immovable in relation to each other with respect to directions vertical to the optical axis of the taking optical system; image signal generation means for generating image signals based on output of the image pickup device; accumulation time control means for controlling charge accumulation time at the image pickup device; pickup image generation means for rendering a plurality of consecutive exposures by controlling the accumulation time control means and for generating one pickup image signal by adding together the obtained plurality of image signals; and motion compensation means for adding together the plurality of image signals after compensated for relative motion among the plurality of image signals in generating the pickup image signal at the pickup image generation means.
In thus constructed image pickup apparatus, a plurality of image signals are added together after compensated for relative motion among the plurality of image signals in generating the pickup image signal. Further, an ordinary imaging block is used without using a special imaging block for shifting a formed image. Hence an increase in size/dissipation-power/cost/etc., and deterioration in image forming performance of the apparatus are not caused and furthermore a high-quality, long-time exposure image taking is possible with also reducing fixed pattern noise. The above object is thereby accomplished.